and cutoff points of tubeworm setting are further verified by the 2-, 

 3-, 4-, 5-, and 6-month panels. Tubeworms did not appear on the 

 2-month panel exposed from April to June, but did appear on the 

 3-month panel exposed from April to July. Tubeworms appeared also 

 on the 4-, 5-, and 6- month panels whose exposure periods began 

 in April. They did not appear on the 2- , 3-, and 6-month panels whose 

 exposure periods began in October, but did appear on the 4- and 

 5-month panels whose exposure periods started prior to October. 

 Thus, tubeworm setting appears to be definitely restricted to the 

 period June through October. Similar consistency is indicated by 

 this diagram for the setting periods of barnacles, jingle shells, 

 hydroids, and bryozoans. 



Figure 15 is a simplified setting period diagram of these forms 

 in this area. The data, of course., are applicable strictly to the 1956-57 

 season; however, the occurrence of the various organisms are expected 

 to follow this general sequence every year with some variation in 

 the beginning and cutoff points. 



Growth, as indicated by the size of various organisms, offers a 

 possiblility for determining the length of time an object has been 

 submerged. Shelled forms such as barnacles, mussels, tubeworms, and 

 jingle shells aid colonial encrusting forms such as bryozoans offer 

 the best possibilities for making such estimates. Figures 16 and 17 

 are plots of the average and maximum sizes of jingle shells and tube- 

 worms for increasing exposure periods. The average and maximum 

 sizes shown on these figures are actually means of the measurements 

 from the various panels. That is, the values plotted for the 1-month 

 exposure period represent the means of the average and maximum 

 sizes of organisms on all panels exposed for 1 month during and 

 subsequent to setting of the organism. Likewise, the values plotted 

 for the 2-month panels represent mean values of the average and 

 maximum sizes of organisms on all panels exposed for 2 months 

 during and subsequent to setting of these organisms. The mere fact 

 a panel was exposed for 3 months does not mean it necessarily 

 represents a 3-month growth period for a particular organism. For 

 example, from Figures 14 and 1 5 it can be seen that the 3- month panel, 

 April to July, actually represents a 1-month period of tubeworm 

 setting and growth. The 4-month panel, April to August, represents 

 a 2-month period of tubeworm setting and growth and a 1-month 

 period of jingle shell and hydroid setting and growth. These facts 

 were considered in determining the values plotted in Figures 16 and 

 17. Jingle shells (Fig. 16) show fairly smooth growth curves for 

 7 months, the longest period of jingle shell growth during this test. 



20 



